Stars · Star in Gemini
Star
Castor
The mortal twin — and not one star but six, in three pairs, all bound together.
- Constellation
- Gemini
- Designation
- α Geminorum
- Apparent magnitude
- 1.58 · 25th brightest star in the night sky
- Spectral class
- A2Vm
- Distance
- 50.9 light-years
- Position (J2000)
- RA 7h 35m · Dec +31° 53′
A white main-sequence star, around 9,500 K, like Sirius and Vega. About 93× brighter than the faintest star the eye can see. The light you are seeing left in 1975.
Discovery
In 1803 William Herschel showed that the two bright stars of Castor had moved around each other: the first proof that stars could orbit each other.